In the related art, a water filtration system only adopts a one-stage filter membrane to filter water, and the water cannot be treated through fine filtration, resulting in unsatisfactory filtration effects, and the water will affect people's health in case of directly drinking. In a water filtration system adopting a multi-stage filter cartridge of the related art, there are disadvantages of a complex conduits, many ports and large volume. In addition, in a process of treating and producing pure water by the multi-stage filter cartridge, waste water is generated, such that a waste water port and a waste water conduit may be disposed separately, making the conduit structure more complex. Moreover water resources are wasted since the waste water is directly discharged out of the water filtration system through the waste water conduit.